1. Field of the Invention
The invention is directed to a fuel injection valve and particularly to such a valve for internal combustion engines.
2. Description of the Prior Art
One known fuel injection valve, known from German Published, Nonexamined Patent Application DE 195 08 636 A1, employs a pistonlike valve member disposed in the bore of the valve body and is axially movable counter to the closing force of a spring. On its end toward the combustion chamber, the valve member has a valve sealing face, which cooperates with a valve seat embodied in the valve body, and as a result at least one injection opening is controlled. The inward- or outward-oriented opening stroke motion of the valve member is defined by a stroke stop. In the closing motion of the valve member away from the stroke stop, the valve member is accelerated in the direction toward the valve seat by the force of the spring. The fuel, which is located between the valve sealing face and the valve seat, has to be expelled in the process. Although this fuel does provide a certain damping of the impact of the valve member on the valve seat, nevertheless the force on the valve member upon impact with the valve seat is still so great that relatively loud engine noise results. Furthermore, in long-term operation, wear can occur in the region of the valve seat, along with incomplete sealing of the injection openings from the combustion chamber.
The fuel injection valve of the invention for internal combustion engines has the advantage over the prior art that the seating of the valve member on the valve seat in the closing motion is additionally damped. Between the portion of the valve member guided in the bore and the oil leakage chamber, a control chamber is provided, which surrounds the valve member over its entire circumference. By means of a pressure face embodied on the valve member, upon the closing motion of the valve member, fuel is expelled from the control chamber through the control bore into the oil leakage chamber, which takes place unthrottled at the onset of the closing motion. In a partial stroke of the valve member, a cylindrical portion of the valve member plunges into the control bore, thus forming an annular throttle gap between the control bore and the cylindrical part of the valve member, through which throttle gap the fuel can now flow out of the control chamber only in throttled fashion. As a result, the seating of the valve member on the valve seat is damped, and the maximum impact forces are reduced. The noise caused by the closure of the valve member is thus lessened, leading to quieter engine operation. Furthermore, the damping leads to reduced wear of the valve sealing face and the valve seat.
Another advantage of the invention is that it can be employed in both fuel injection valves that open inward, away from the combustion chamber, and in fuel injection valves that open outward. All that is needed is to transpose the disposition of the control piston and the control bore.
The outflow of fuel from the control chamber need not take place exclusively via the annular throttle gap. In a further version, it can also be provided that additional throttling conduits are embodied in the valve body or in the valve member that connect the control chamber to the oil leakage chamber. This also makes it possible for the throttling action of the control chamber to be regulatable via adjustable throttle connections.
In both versions, the spring loading the valve member is disposed in the oil leakage chamber, which has an outflow conduit through which the fuel is carried back into the tank via an outflow line. The outflow rate of the fuel from the control chamber depends not only the flow resistance of the throttle connection to the oil leakage chamber but also on the pressure difference between the oil leakage chamber and the pressure chamber. If the pressure of the fuel in the oil leakage chamber is relatively high, then the outflow of fuel from the control chamber will proceed more slowly than at low pressure. As a result, a higher pressure can build up in the control chamber, which via the higher pressure on the pressure face damps the seating motion of the valve member more markedly. By the provision of a pressure holding valve in the outflow conduit of the oil leakage chamber or in the outflow line, a previously determined pressure can be maintained in the oil leakage chamber. The outflow rate from the control chamber and thus the damping action of the control chamber can thus be varied by way of the holding pressure. If the pressure holding valve is embodied in regulatable form, then the damping action can be adapted to given requirements as a function of the engine operating state.